Architectural design and fiber‐type distribution of the major elbow flexors and extensors of the monkey (cynomolgus)

Abstract

Because the architectural and biochemical properties of skeletal muscle dictate its force, velocity, and displacement properties, the major extensors (triceps brachii) and flexors (biceps brachii, brachialis, and brachioradialis) of the elbow in a primate (cynomolgus, monkey) were studied. Functional cross-sectional areas (CSA) were calculated from muscle mass, mean fiber length (normalized to a 2.20 microns sarcomere length), and angle of fiber pinnation measurements from each muscle. Fiber-type distributions were determined and used as a gross index of the biochemical capacities of the muscle. The extensor group had a shorter mean fiber length (31 vs. 47 mm), a larger CSA (13 vs. 8 cm2), and a higher overall percentage of slow-twitch fibers (47 vs. 26%). Consequently, the elbow extensors had a relatively greater potential for force production and force maintenance than the flexors. In contrast, the flexors were designed to optimize their length-velocity potentials; i.e., they had relatively long fibers and a higher fast-twitch fiber composition than the extensors. These morphologic differences between antagonistic muscle groups should be considered when evaluating the motor control mechanisms regulating reciprocal movements about the elbow.

Histochemistry profile of the biceps brachii muscle fibres of capuchin monkeys (Cebus apella, Linnaeus, 1758)

“…Whereas percentages of FG and SO fibres vary from surface to deep regions within a certain muscle (Schmidt and Schilling, 2007), the percentage of FOG fibres remains constant in these regions as is observed in the cynomolgus monkey (Roy et al, 1984;Singh et al, 2002) and in the biceps brachii of the capuchin monkey in this study.…”

“…The deep regions are mainly composed of SO fibres, indicating a stabilising function, whereas the surface regions have a higher proportion of FG fibres and are therefore most appropriate for mobilisation (Schmidt and Schilling, 2007). These characteristics of muscle fibre type distribution are true both for the muscles of the members, as well as for those of the trunk (Ariano et al, 1973;Collatos et al, 1977;Armstrong, 1980;Burke, 1981;Roy et al, 1984;Petter and Jouffroy, 1993;Jouffroy et al, 1999;Schilling, 2005;Schmidt and Schilling, 2007).…”

Muscle Maintenance by Volitional Contraction against Applied Electrical Stimulation

“…For example, an investigation by members of this group found that the MF and MPF slopes in the triceps brachii of wheelchair marathoners displayed an improved endurance relative to wheelchair naïve ambulatory control subjects [20]. It is also significant that another recent upper extremity study [28] has revealed that the fast twitch fiber rich biceps reveals a steeper degradation in its firing frequency than the slow twitch rich triceps [21,22,26].…”

“…two muscles were stimulated at the same relative intensity (threshold intensity + 2/3rds the difference between the maximum comfortable intensity and the threshold intensity). It is possible that the reason for the difference may lie in the different fiber composition of the two muscles: the triceps has a higher proportion of slow twitch fibers than the biceps in monkey [21,22], and at least one recent report has suggested that gains in strength by electrical stimulation in fast twitch rich muscles comes at a cost of decreased endurance in human lower extremities [17]. The finding that the fatigue resistance of the triceps in the HYB Group improved with training while that of the ELS Group worsened may have a similar root cause.…”

Skeletal muscle design to meet functional demands

“…Additionally, while there is a great deal of variability in muscle architecture between muscles within an individual, there is consistent architectural design within muscles among individuals. This can be seen by the fact that published between-individual variability is relatively small within the hindlimbs of a given species [17][18][19][20][21][22][23][24][25].…”